1. Field of the Invention
The present invention relates to handling of multi-chip modules (MCMs) to facilitate automated testing and sorting thereof and, more specifically, to an automated module handler adaptable to handle different types and configurations of such modules in cooperation with a variety of testers which may be associated therewith, as well as the method of operation of the handler.
2. State of the Art
Production and quality demands of the computer industry, and particularly the personal computer industry, have compelled automation of component testing with ever-higher throughputs. Individual semiconductor dice are at least subjected to a nominal level of testing and burn-in prior to being mounted on carrier substrates such as printed circuit boards, and complete testing and characterization of dice to qualify what are termed xe2x80x9cknown good diexe2x80x9d or xe2x80x9cKGDxe2x80x9d is becoming more prevalent, although by no means a standard procedure. Over and above the testing of individual dice, however, is the requirement that a multi-chip module, comprising a carrier substrate, such as a circuit board bearing a plurality of dice thereon, be tested and characterized as an operational unit before being installed in a personal computer, either as original equipment or as part of an upgrade.
One particularly common type of multi-chip module is a multi-chip memory module, wherein a plurality of memory dice is mounted to one or both sides of a carrier substrate, which is then installed in a card slot in a personal computer chassis to provide or upgrade the memory capacity of the computer by connection of the module to the computer motherboard bearing the processor and logic circuits. The most common types of memory modules are currently Single In-line Memory Modules (SIMMs) and Dual In-line Memory Modules (DIMMs). Both SIMMs and DIMMs employ multiple pin edge connectors running along a single edge of the carrier substrate, the edge connectors providing electrical connections to the motherboard through the chassis of the computer. The edge connectors may include a single set of contacts extending about the edge, as in the case of a SIMM, or discrete contacts on each side of the carrier substrate adjacent the edge to provide more separate contact locations, as in the case of a DIMM.
As noted above, it is required that multi-chip modules, including without limitation memory modules, be tested prior to installation to ensure that they will be fully operational. Module handlers have been developed to automatically present modules to a testing device or xe2x80x9ctesterxe2x80x9d, which conducts the test of a module, the results of which test, in comparison to criteria preprogrammed in the tester, dictate the sort category of the module. The sort categories are conventionally either xe2x80x9cpassxe2x80x9d or xe2x80x9cfailxe2x80x9d, although sorting into operational sub categories depending on variations in operational module performance is becoming more common. Handlers may include a hopper or tray into which a plurality of modules is preloaded before placement on the handler, which then feeds one module at a time to a test site for testing through the multiple pin edge connector of the carrier substrate, and subsequently, to a receptacle based upon the module""s exhibited test characteristics.
Handlers, and specifically the module conveyance systems thereof, are ideally reconfigurable to accommodate different thicknesses of modules, the term xe2x80x9cthicknessxe2x80x9d being used herein to denote the dimension of a module perpendicular to the plane of the carrier substrate, termed a xe2x80x9ccardxe2x80x9d or xe2x80x9cprinted circuit boardxe2x80x9d. Module thickness depends in part on carrier substrate thickness, in part on the height of the dice (including packaging) carried by the carrier substrate, and in part on whether dice are mounted to one or both sides of the carrier substrate. Many prior art handlers are only reconfigurable to accommodate different module thicknesses through extensive and complex removal and replacement of a substantial number of parts, which takes time and often requires the use of various tools.
One relatively simple approach to handler conveyance system reconfiguration is disclosed in U.S. Pat. No. 5,667,077, wherein an existing module handler conveyance channel is made reconfigurable to accommodate thicker or thinner modules through the insertion within the channel of one of a plurality of different-thickness, removable, justifying plates, the channel being sized to accommodate the thickest module contemplated for testing by the absence of any justifying plate whatsoever. The handler type to which the modifications are suggested, exemplified by the MC Systems, Inc. Model 828-MCM and Model 838-SIMM/DIMM Module Handlers, includes a vertical magazine or hopper which feeds modules to a belt-driven conveyance system employing the aforementioned variable-width channel to transport the modules in series to a test site and then to receptacles in a plurality of sort categories. Disadvantages of such an apparatus include the need for a large number of justifying plates if modules of a wide variety of thicknesses are to be tested, the practice of physical stacking of modules on top of one another (which may lead to damage), inability to ensure precise module alignment entering the conveyance system, lack of a positive grip on each module as it is conveyed to the test site (which may present alignment and jamming problems), lack of positive engagement and alignment of each module with the test contacts at the test site, and the lack of a positive and certain displacement of each tested module from the test site when it is to be moved toward the sort receptacles.
Another approach to module handlers is exhibited by the Exatron, Inc. Model 3000B SIMM/DIMM Handler, which employs gravity feed of singulated modules from a magazine along an inclined track to a test site, after which a tested module either slides directly into a bin of the appropriate sort category or into an output arm over a movable tray, the arm opening to release the module into a slot of the tray when aligned therewith. This handler is very operator time-intensive as it fails to provide a mechanism for receiving a large number of modules for test as it is limited to a single hand-loadable magazine of a set configuration fixed to a carriage on the handler, fails to provide positive retrieval of modules from the magazine and placement at the test site, fails to provide positive alignment of the modules at the test site, fails to provide positive displacement of a tested module from the test site, and does not appear to be quickly or easily adaptable to modules of varying thicknesses.
In short, conventional multi-chip module handlers suffer from insufficient automated input capacity, as well as a lack of positive module retrieval and placement at the test site, positive module alignment for test, and positive displacement of a tested module from the test site for sorting. Finally, the adaptability of conventional handlers to various types of modules is limited and cumbersome.
The method of handling multi-chip modules (MCMs) according to the present invention overcomes the above-enumerated deficiencies of conventional handlers and provides numerous additional advantages.
The inventive method may employ (module) type-specific magazines which the operator may load with modules prior to placement on the handler, the magazines being vertically stackable at both magazine input and magazine output stations, each magazine being moved horizontally as it reaches the bottom of the input stack by a positive drive system which carries the magazine through the indexing station for module retrieval and to the output station, where it is again stacked, this time under the next-previous emptied magazine. Further, according to the inventive method, each module is positively retrieved from its magazine and transferred to the test site. This may be accomplished by an indexer which guides each module and carries it to the test site, reducing any tendency toward jamming in comparison to handling methods which rely on gravity to index and/or transfer the MCMs to a testing site. Once at the test site, positive module location for testing is effected using locating pins which engage the module""s pre-existing tooling holes in the carrier substrate to exactly align the module relative to the test contacts. Once testing is completed, positive ejection of the tested module from the test site to an output track is effected by the indexer""s arrival at the test site with another module for test, again reducing the jam rate in comparison to conventional gravity-feed handling methods. Once tested, a module is consigned by the output track either to a shipping tray if it passes testing or to a fail bin if it does not. The method may include the use of dual-row trays of various types, the tray when mounted on the handler being borne by a carriage moving transversely under the path of the tested module to receive each test-passing module from a stop position on the output track into an empty tray receptacle, or slot. The method is amenable to many module types and configurations and is easily adapted from use with a first type of module to a second type of module.